Out of Order Execution

• allow the processor to avoid a class of delays that occur when the data needed to perform an operation are unavailable
• Instruction fetch.
• Instruction dispatch to an instruction queue (also called instruction buffer)
• The instruction waits in the queue until its input operands are available.
• The instruction is issued to the appropriate functional unit and executed by that unit.
• The results are queued (Re-order Buffer).
• Only after all older instructions have their results written back to the register file, then this result is written back to the register.